Manufacture of stratified blocks of plumbago.



CHARLES \VILLIAM SPEIRS,

OF BATTERSEA, LONDON, ENGLAND, ASSIGNOR TO THE MORGAN CRUCIBLE COMPANY, LIMlTED, OF BATTERSEA, LON- DON, EN GLAND.

MANUFACTURE OF STRATIFIED BLOCKS OF PLUIV IBAGO.

Specification of Letters Patent.

Patented Oct. 3, 1905.

Application filed May 22,1905. $eria1 No. 261,690.

To all whom it may concern.-

Be it known that 1, CHARLES \VILLIAH Srnms, a subject of the King of Great Britain, residing at Battersea IVorks, Battersea,

5 London, England, have invented a new and useful Manufacture of Stratified Blocks of Plumbago, of which the following is a specilication.

My invention relates to the manufacture of blocks of compressed plumbago having a stratified character which specially adapts them for use for certain purposes, such as commutator-brushes, bearing-surfaces, plungers or pistons, and the like, in which a dif- I ferentiation of structure in different directions is desirable.

I have discovered that if natural plumba-go of the crystalline or flaked variety is ground and then strongly compressed the flakes or crystals (which are of more or less laminated structure) tend to set themselves in planes parallel to the plane of pressure and are capable of adhering under such conditions and forming a solid block of a stratified character whose electrical properties, wearingproperties, and other physical properties in the direction of the line of pressure and of lines at right angles-thereto are very different. I believe that this stratification is in part due to 3 the effect of the laterally-escaping air upon the flaky particles. This differenceis ofgreat importance for some purposes. For instance, for certain electrical purposes it may be of great advantage to be able to produce a solid coherent plumbago structure of any desired size or shape, which has a relatively high conductivity in one direction and a low conductivity in transverse directions. Moreover, for certain wearing purposes it is an advan- 4 tage to have a material in which the flakes or crystals are so directed that the wearing-surface may be formed in'a direction at right angles to the planes of the flakes, or nearly so.

7 According to my invention I make use of crystalline or flaked natural plumbago-for example, of the kind which is mined in Ceylonand I grind this substance to a suitable degree of fineness. Crystalline plumbago differs from amorphous plumbago in the flaky or laminated character of the structure even in the state of powder. The plumbago should be ground to a powder which will pass through a sieve having, say, one hundred meshes to the linear inch. The plumbago is then compressed in suitable molds under a pressure of not less than about twenty tons to the square inch and is thus converted into solid blocks of the desired shape. The plumbago flakes when the pressure is applied set themselves in planes at right angles to the direction of such pressure that is to say, with their larger surfaces parallel with the pressure-surface. The plane of pressure must be suitably directed with reference tothe purpose for which the block is required, or the block must be cut and finished, with the lines of stratification arranged with reference to such purposes. For instance, for commutator-brushes the lines of stratification should run in the direction of flow of the current. For wearing surfaces the planes of stratification should be at right angles to the wearing surface.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is 1. The method of manufacturing solid stratified blocks of plumbago, which consists in grinding crystalline or flaked natural plumbago to a suitable degree of fineness and then subjecting the ground plumbago to such a high degree of pressure as will cause the flakes to set themselves in stratifled planes, parallel to the line of pressure, substantially as described.

2. The method of manufacturing solid stratified blocks of plumbago, which consists in grinding crystalline or flaked natural plumbago to a suitable degree of fineness and then subjecting this ground plumbago to a pressure of approximately twenty tons to the square inch, substantially as described.

CHARLES WILLIAM SPEIRS.

Witnesses:

A. R. BOSMAN, A. ALBUTT. 

